Flexible packages and bags are used for containing and storing a wide variety of materials. Although the invention has application to many different types of packaging, it is particularly suited for bags that are used to package snack foods and other food products and that are composed of thin cellophane or organic polymer base plastic materials that have limited tear resistance once a tear starts.
Hundreds of millions of such bags are made each year. They are manufactured in a combined form-and-fill apparatus in which the sheet packaging is drawn past a guide which directs the material into a tubular form surrounding a mandril. As the material is drawn along the mandril, an overlapping or fin-type longitudinal seal is formed in the material sealed by a heat or pressure sealing process. The material is thus formed into a continuous tube as it passes over the mandril. The material then feeds two heat sealing jaws that are disposed to form a transverse sealing area across the tube thereby to form simultaneously a top seal in one bag and a bottom seal on an adjacent bag. When this occurs, the apparatus feeds a measured amount of the snack food or other material into the bag having the bottom seal through a passage in the mandril. The tube is then advanced to bring the top of the just-filled bag opposite the sealing jaws and the jaws are actuated to form another sealing area which includes a top seal in the just filled bag and a bottom seal in the next bag to be filled. Accordingly, each sealed bag contains a longitudinal seal and transverse seals at its opposite ends which define a hermetically sealed pouch or package for the snack food or other contents. The sealing jaws normally also contain a mechanism for severing each bag after it is filled and sealed from the tube of packaging material so that the severed bag can be advanced to an appropriate location to prepare it for bulk shipment to its ultimate destination. This form and fill manufacturing process is widely used and accepted because it is reasonably simple, requires a minimal number of operations and has proven over the years to be quite reliable.
However, bags and packages formed by this process are not without their problems as purchasers of snack foods and other material contained in such bags are well aware. Some of the bags can be difficult to open because the plastic material of which they are made is highly resistant to puncture. Typically, a purchaser will attempt to open such a bag either by tearing through the seal or by trying to separate the seal. When an attempt is made to tear through the seal, the user finds it very difficult to start the tear. Indeed, it is not unusual for the user to chew the bag in an attempt to tear the bag's seal. However, once a tear is started, the direction of such a tear and the length of the tear are more or less random. The nature of such packaging material is that the tear could travel in any direction along the bag wall and, depending upon the force utilized to start the tear, could travel for various distances along that wall. In extreme cases, the tear can propagate all the way down one side of the bag allowing the bag contents to spill. On the other hand, if the purchaser grabs the opposite walls of the bag and tries to pull the walls apart to separate the top seal from below, a random opening can also occur. That is, the force required to separate that seal varies widely and is not predictable. Consequently, in some cases, the purchaser may pull the walls apart with too much force with the result that the bag tears and spills its contents.
In many cases, also, these bags contain perishable contents and such contents become stale if exposed too long to air. Therefore, if the contents of such bags are only partially consumed, it is not easy to reclose the bags with sufficient tightness to preserve the freshness of the remaining bag contents. Usually, the purchaser is left to twisting or rolling up the open end of the bag, assuming that remains intact when the bag is opened. However, at best, the bag material, having a memory, tends to resume its original shape and the rolled or twisted portion of the bag tends to straighten sufficiently to expose the bag contents to air. It is thus difficult to effectively reclose a plastic package or bag of this type without some separate closure element which, as a practical matter, adds to the bag cost and often becomes lost.
Considerable research and development has been expended in order to provide a bag or package of this general type which is easy to open and yet which can be reclosed simply and conveniently. Indeed, some bags have been designed in an attempt to solve both the opening and reclosing problems affecting such bags. Generally, these bag designs include some structure for assisting or directing the opening by tearing of the bag and some element formed integrally with the bag, but which is removable from the bag, so that the element can be used to reclose the bag if the bag contents are only partially consumed. For example, U.S. Pat. No. 3,184,149 discloses a resealable bag. This bag includes a sheet of flexible material having a structure for cutting through the side of the bag to expose the contents for consumption or use. If the contents are only partially utilized, a protective layer formed in a top seal portion of the bag is removed to expose a coextensive area of adhesive material. When the top of the bag is folded down against itself, the adhesive material adheres to the bottom seal to close the bag. U.S. Pat. No. 3,224,640 discloses a bag having at least three walls. The contents are stored in a pouch between the first and second walls. The bag includes a tear line which extends partially through the seal. As the top is torn off the bag, the contents are exposed. A slit is formed in the third wall to receive the top of the bag after it is folded over. U.S. Pat. No. 3,618,850 discloses a bag in which a pleated foil strip is affixed to the bag just below one end of the end seal. The bag is opened by tearing through the seal. The foil serves as a tear stop and it guides the tear transversely across the bag. If the bag contents are only partially consumed, the top of the bag can be folded about a transverse axis that passes through the foil. The pleats in the foil then tend to retain the folded shape of the foil and thereby keep the bag closed.
Another group of bag designs are characterized by a tear strip that can also be used to reclose the bag. U.S. Pat. Nos. 3,311,288 and 3,426,959 disclose such bags. More specifically, a tear strip is affixed transversely across the bag into one wall in the area of the pouch. When the tear strip is pulled, it rips the bag under the tear strip and exposes the bag contents. Once the tear strip has been removed, it can be saved to reclose the bag by being wrapped around the bag. U.S. Pat. No. 3,480,198 discloses a bag in which a tear line is formed across the bag in one or both walls of the bag inwardly of the heat seal; that is, the tear line is on the walls that are separated to form the pouch for the bag contents. The tear line is formed by apertures through both side walls that are fused around their edges so that the seal is not broken until the bag is torn along the tear line. The top segment of the bag can thus be removed to form a tie for the bag to seal in the remaining contents. However, this action does not open the bag completely.
U.S. Pat. No. 3,613,874 shows a bag in which a pressure sensitive adhesive is applied as in the case of the bag in the aforementioned U.S. Pat. No. 3,184,149. A tear strip is also provided to tear away a portion of the bag. That tear strip has a relatively high tensile strength and it is bonded rather strongly to the film forming the bag in such a way that the strip will not break or pull away from the film, but will overcome the film's tear strength when it is pulled away thereby tearing the bag.
U.S. Pat. No. 3,619,395 shows a plastic bag with a tear strip in the form of a ribbon which is pulled to tear the bag. This bag contains a releasable fastening means on the inner, opposite wall surfaces of the bag which enable the bag to be resealed.
U.S. Pat. No. 3,674,135 treats separately the problem of reclosing a previously opened bag. It discloses a roll of plastic bags sequentially dispensed from a carton. The roll comprises a two-ply strip of plastic sealed along its sides to form a tube. The two plies are also joined by a series of pairs of transverse seals one of each said pair defining the bottom of a bag. A series of pairs of perforations are located adjacent said pairs of seals (i.e., interfitted therewith) for separating sections of the strip to define the open top of a bag and to separate a closure band defined by each said pair of spaced perforations. However, the perforations are disclosed as straight slits or as saw tooth cuts in the bag material which encourage uncontrolled tearing of the bag walls. They also encourage tearing of the closure band when the band is separated from the body of the bag and tensioned in use. Further, the transverse seals formed in the strip are flat so that the closure band is not otherwise as strong as might be desired.
The individual problem of facilitating the opening of these bags has also been addressed separately. One general approach for solving the problem can be characterized as providing tabs above the seal or outside the seal for facilitating the opening. This approach is exemplified in U.S. Pat. Nos. 3,397,835 and 3,419,137, as well as in British patent No. 620,354. In the bag shown in the first such patent, for example, a bag corner portion or inset is heat-sealed and includes a tear line. To open the bag, the portion of the bag outside the tear line is removed. Then the opposite walls of the bag in the inset, which are not sealed together, can be grasped individually to facilitate opening the bag. Another approach has been to add structure to the bag that will limit or direct the tear during the opening of the bag.
Folding the bag material to produce folded portions around the bag are shown in U.S. Pat. No. 4,053,116. The use of transverse beads to limit the tear is shown in U.S. Pat. Nos. 3,323,707 and 4,139,643. Other examples of such bags are disclosed in U.S. Pat. Nos. 2,023,855; 3,142,918 and 3,179,327. The use of special chemical treatments by placing a coating between the heat-sealed surfaces of the bag before bonding to facilitate opening is shown in U.S. Pat. No. 3,511,436.
None of the aforementioned prior bag configurations have gained wide, if any, commercial acceptance. Many of them are characterized by being more expensive to manufacture than a conventional bag or involve manufacturing techniques that are unfamiliar to the industry which is therefore reluctant to adopt them. Most importantly, the prior packages and bags which incorporate pull-apart finger openings and/or a removable reclosure tie incorporated into the bag still suffer uncontrolled tears when the purchasers try to use the easy-opening feature or to remove the reclosure tie for use. Indeed, the problem of uncontrolled tear propagation in such packages and bags has effectively prevented manufacturers from incorporating an easy-opening, pull-apart feature or a removable reclosure tie feature into bags and packages of this general type at a reasonable cost. In other words, those prior bag designs which are cost effective have not been able to reliably control the tearing of the bag walls which occurs when the purchaser tries to use the easy-open or reclosable feature of such packages and bags, with the result that the bags split and tear apart to the ultimate annoyance of the purchaser.
Relatively recently, bag designs have been developed that do incorporate an easy open feature as well as a reclosing feature and which can be manufactured at reasonable cost by more or less standard forming and filling apparatus, using techniques and procedures familiar to the packaging industry. Such bags and the apparatus for making them are disclosed in U.S. application Ser. No. 451,170, filed Nov. 29, 1982, entitled EASILY OPENED AND RECLOSABLE BAG AND APPARATUS FOR MAKING SAME, now U.S. Pat. No. 4,540,657, owned by the assignee of the present application. While those bags do work well and represent a significant improvement over previous such designs, they still do not provide optimum results at least with some bag materials. That is, the bags made in accordance with the techniques disclosed there occasionally still do suffer random tearing. This is especially so in the case of bags made of the laminated plastic materials and metalized plastic materials most preferred by the food industry for packaging snack foods such as potato chips, candy, popcorn, etc. and which are characterized by high puncture-resistance but low tear resistance. A typical such material is a lamination of at least two sheets of different-thickness polypropylene films bonded together by a film of polyethylene.
Apparently, this unwanted tearing is due to the fact that when the individual bags are formed and separated from the continuous tube of packaging material, tiny tear sites are created in the cut edges of the bag material each of which promotes or encourages the start of an unwanted and undirected tear in the bag walls. Some of these tear sites are present at the upper edge of the bag and promote uncontrolled tears at that location when the user tries to open the top seal of the bag, even if that seal includes pull-open tabs intended to facilitate breaking the seal. Some such sites are present at the bottom edge of the bag or at the locations in the bag walls which are perforated to form the parting or separation line along which the reclosure tie is separated from the bag. Tears started at those locations sometimes propagate destructively along the bag walls thereby exposing the bag contents or into the reclosure tie thereby weakening the tie with the result that the tie breaks when tensioned in the process of reclosing the bag.
In addition, we have found that when the reclosure tie is separated from the rest of the bag for use, the separation process itself sometimes produces tear sites in the bag material along the reclosure tie parting line which promote uncontrolled tearing and weakening of the bag itself and/or its reclosure tie. The separable reclosure ties in those prior bags are somewhat disadvantaged in other respects in that they are not as strong as might be desired and sometimes they are difficult to release or untie after they have been used to reclose the associated bags.